The present invention relates to a back metal equipped to a disk brake mounted on a vehicle or an industrial machine etc., that supports a friction member used in a brake pad with variable pressure from the surface of the friction member that is not in contact with a rotor, and the method of manufacturing the same.
Heretofore, in the case of a single cylinder type disk brake, the disk brake comprises as shown in FIG. 13 a disk rotor (hereinafter called rotor) 1, friction members 2, 2 that sandwich the periphery of the rotor and constitutes a brake pad, and back metal plates 3, 3 that are adhered to the side of each friction member that is not in contact with the rotor. Further, the end surface of a brake piston (hereinafter called piston) 4 contacts one of the two back metal plates 3 on the opposite surface to where the friction member contacts, and a cylinder 5 housing the piston 4 is connected to a caliper 6, the upper end of the caliper 6 placed so as to bridge over the outer peripheral of the rotor 1. The back surface of the other back metal plate is adhered and fixed to the surface of the caliper 6 facing the rotor.
The inner surface of the cylinder 5 is carved so as to create a seal groove 5a for fitting a seal ring 7 for preventing the pressure oil from leaking and a seal groove 5b for fitting a dust boot 8 acting as dustproof seal to be placed between the piston and the cylinder.
The back metal plate 3 can be formed by perforating a steel plate with a press so as to create a predetermined back metal plate shape having flat front and back surfaces with holes (perforations) 3d, 3d formed thereto as shown in FIG. 14, or having either concavity and covexity or dimples formed to the surface that contacts the friction member 2.
[Problems]
Since the conventional back metal plate 3 for a disk brake is required to have enough strength to endure pressure, a flat-shaped steel plate is normally used.
The deformation of the back metal plate 3 causes dragging, brake noise, deterioration of the feeling of the brake and so on. In order to prevent deterioration of the back metal plate 3 by changing the material being used, the cost for material of the back metal plate becomes too expensive.
On the other hand, since the pressure surface of the back metal plate 3 comes into contact with the piston 4, the heat generated at the friction portion is transmitted from the back surface via the piston 4 to the brake fluid, thereby raising the temperature of the brake fluid, and in some cases even causing vapor lock. Therefore, when the disk brake is to be used for special purposes, means for preventing the excessive temperature rise of the brake fluid must be applied to the disk brake, such as inserting a heat insulator between the piston 4 and the back metal 3.
The present invention aims at providing a solution for the problems of the prior art product. The object of the present invention is to provide a back metal plate of a disk brake pad and the method of manufacturing the same, the back metal plate having an improved bend strength without having to rely on any special material, having advantageous heat radiation property without adding any insert, thereby enabling to suppress excessive temperature rise of the brake fluid.
In order to solve the problems of the prior art effectively, the present invention provides in claim 1 a back metal plate of a disk brake pad comprising a plurality of dimples each having a substantially spherical surface with a portion being overlapped to one portion of another dimple, said dimples formed to at least either a front surface or a back surface of a plate member; flat portions surrounded by said dimples, the upper surfaces of which constituting the same surface as said plate surface; and boundary portions formed to the areas where said dimples overlap, which are lower than said flat portions but higher than the bottom portion of said dimples.
According to this invention, boundary portions each having a substantially square-shaped flat surface surrounds each dimple, thereby increasing the bend strength of the back metal plate, and realizing a relatively lightweight back metal plate. The dimples are formed to the whole surface of the back metal plate creating a wavelike cross-section, and the remaining flat portion where no dimples are formed becomes the contact surface with the piston, the contact area between the piston and the surface of the back metal plate being reduced with gaps formed thereto, enabling air to flow through the boundary portion between the dimples and helping heat radiation, thus reducing the heat being conducted to the piston and preventing excessive temperature rise of the brake fluid.
Further, the present invention provides in claim 2 a back metal of a disk brake pad in which the depth of the dimples is in the range of 0.3 to 1.5 mm. This improves the reinforcing effect of the back metal plate.
The back metal plate of a disk brake pad according to claim 3 characterizes in that the dimples are formed to both front and back surfaces of the back metal plate, the dimples on one side being positioned so as to oppose to the dimples on the other side. This feature enables the reinforcement effect of the back metal plate to be realized effectively by the boundary portions being protruded at the same positions on the front and back surfaces of the back metal plate.
Moreover, the back metal plate of a disk brake pad according to claim 4 of the present invention is characterized in that the dimples are formed to both front and back surfaces of the back metal plate, the pitch of the dimples formed on one side being displaced from the pitch of the dimples on the other side. This feature of the invention provides a back metal plate having a substantially even thickness with increased strength.
The method for manufacturing the back metal plate of a disk brake pad comprises forming the dimples mentioned in any one of claims 1 through 4 by cold-working a plate material using coining. Providing dimples to a plate surface by cold-pressing hardens the plate material and the boundary portions formed between adjacent dimples act as reinforcement members improving the bend strength of the back metal plate. Thus, the bend strength of the back metal plate is increased without increasing the plate thickness of the back metal plate. The process to create dimples to the whole surface of the back metal plate forms flat portions surrounded by the dimples and boundary portions formed to the area where the dimples overlap, by which the cross-sectional shape of the back metal plate becomes wavelike. This wavelike cross-section of the back metal plate prevents the whole contact surface of the back metal plate from coming into contact with the piston, limiting the area of contact to the boundary portions surrounding the dimples and the flat portions, the concaved portions of the boundary portions creating gaps to the contact area, through which air is flown, helping heat radiation. This gap further suppresses the amount of friction heat generated at the time of braking from being conducted to the piston through the back metal plate, and thereby prevents the brake fluid from being heated excessively.
Moreover, the method for manufacturing the back metal plate of a disk brake pad according to claim 6 is characterized in that the dimples according to any one of claims 1 through 4 are formed by a rolling process. According to this method, the metallographic of the plate material being pressed by the rollers is plasticized, and a back metal plate having predetermined sized dimples is created.